Variation in nectar–sugar profile of Anchusa and allied genera (Boraginaceae) MASSIMO NEPI 1 *, FEDERICO SELVI 2 and ETTORE PACINI 1 1 BIOCONNET, Biodiversity and Conservation Network, Department of Environmental Sciences ‘G. Sarfatti’, University of Siena, Via Mattioli 4, 53100 Siena, Italy 2 Department of Plant Biology, University of Florence, Via La Pira 4, 50121, Florence, Italy Received 17 September 2009; accepted for publication 10 February 2010 The nectar–sugar profile (fructose, glucose and sucrose) of 14 species of Anchusa and five members of the allied genera Anchusella, Cynoglottis, Hormuzakia and Lycopsis (Boraginaceae: tribe Boragineae) was determined. Most of the species examined (c. 74%) produce sucrose-dominant nectar, whereas the remaining taxa produce sucrose- rich nectars. Little variation in nectar–sugar composition was found in some species, even when sampling was repeated in different years and/or localities. Average sucrose concentration was 57.75% (coefficient of variation 19.1%). The only floral morphological character that was correlated with the nectar–sugar profile is the length of the corolla tube, as taxa with relatively long floral tubes produce nectar with lower glucose concentrations. The flowering period is also related to sugar composition, as nectar of late-flowering species contains lower sucrose concentrations. However, small differences in sugar profiles do not reflect phylogenetic relationships based on molecular studies. It would appear that dry habitats and time of flowering are the main determinants of nectar–sugar composition in the genus Anchusa sensu lato. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162, 616–627. ADDITIONAL KEYWORDS: Boragineae – flower morphology – nectar–sugar composition – pollinators. INTRODUCTION Nectar is a complex mixture of substances dissolved in water and is a nutritive source for a large number of animal species (Nicolson, 2007; Nicolson & Thornburg, 2007), although in some instances its function may be much more than a simple, floral reward (Thornburg, 2007; Nepi & Stpiczyn ´ ska, 2008). Sugars (mainly glucose, fructose and sucrose) are the major solutes found in floral nectar. In an extensive study of the nectar–sugar composition of 765 species of angiosperms, Baker & Baker (1983a) found that sucrose was present in 89% of the species examined and 84% had nectar containing all three sugars. It is generally accepted that there exists a co-evolutionary relationship between the proportion of sugars in nectar and the dietary preferences of pollinators and that this, in turn, has led to convergence in sugar–nectar composition in unrelated species visited by the same type of polli- nator (Baker & Baker, 1983a, b; Nicolson & Thorn- burg, 2007). Flowers pollinated by long-tongued bees, butterflies, moths, hummingbirds and Old World bats tend to produce sucrose-rich nectars, whereas those pollinated by flies, short tongued- bees, perching birds and New World bats tend to produce hexose-rich nectars (Baker & Baker, 1983b). However, it has been demonstrated that deducing pollination syndromes from nectar types is often too simplistic (Barnes, Nicolson & van Wyk, 1995). Phy- logenetic conservatism governing nectar–sugar com- position has also been demonstrated for several angiosperm taxa, such as Lamiaceae, Ranuncu- laceae, Brassicaceae (Baker & Baker, 1983a; Petani- dou, 2005), Alooideae (van Wyk et al., 1993), Papilionoideae (van Wyk, 1993) and Proteaceae (Nicolson & van Wyk, 1998). Within these broad *Corresponding author. E-mail: massimo.nepi@unisi.it Botanical Journal of the Linnean Society, 2010, 162, 616–627. With 3 figures © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162, 616–627 616 Downloaded from https://academic.oup.com/botlinnean/article-abstract/162/4/616/2418445 by guest on 12 June 2020